1. Field of the Invention
The present invention applies to a slot structure in a repeating frame used in time division communications between base stations and user terminals and, in particular, to a slot structure that allows different types of messages to be transmitted interchangeably in the same slot.
2. Description of the Prior Art
Time division mobile radio communications systems such as cellular data and voice radio systems typically use a repeating frame that includes slots allocated for specific purposes. In a frequency division TDMA (Time Division Multiple Access) system, the repeating frame may include a set of downlink slots. A set of uplink slots is in another frame on a different frequency. Broadcast, random access and control channel messages may each be assigned to specific frequencies that use a different frame structure. Within each frame, the slots for each type of message can be optimized for the type of messages that it carries enhancing efficiency. In a TDD (time division duplex) system, uplink and downlink slots are in the same frame. In some instances, specific slots within the frame may carry some control messages. However, the control and access channels are normally in specifically optimized slots in separate frames.
Separate broadcast, control and access channel slots allow great flexibility in designing a wireless radio network of base stations and remote user terminals. However, each channel that is set aside for broadcast, control or access purposes cannot be used for traffic. When the number of channels is limited in comparison to the demand for traffic, it is preferred to maximize the traffic usage of all of the system's radio capacity.